PIK3CA and breast cancer: In addition, as patients in E20 group had a longer OS and RFS than those in E9 group, studies in breast cancer had found clinical significance between patients with mutations in helical (exon 9) and kinase (exon 20) domain with inferior overall survival in those with mutation in the helical domain [40].These observations are also supported by findings in soft tissue sarcoma in which downstream activation level of PI3K is higher in tumors with helical domain mutations than those with kinase domain mutation [41].